Coleoptera, Hydrophilidae) in South-Western Iberian Peninsula

PATIERNS OF SMALL AND LARGE-SCALE SPATIAL DISTRIBUTION OF COPROPHILOUS SPHAERIDIINAE (COLEOPTERA, HYDROPHILIDAE) IN SOUTH-WESTERN IBERIAN PENINSULA

E. ROMERO-ALCARAZ *, F. SÂNCHEZ-PINERO ** & J.M. ÂVILA*

RÉSUMÉ

Lors d'un cycle annuel, on a utilisé des pièges appâtés par des excréments de bovins, pour étudier la distribution spatiale de quelques espèces de Sphaeridiinae (Col. Hydrophili dae) dans deux biotopes (prairie et savane), d'une ferme d'élevage située à Chiclana de la Frontera (Cadiz, Espagne). Toutes les espèces capturées (14 au total) se trouvaient dans les deux biotopes considérés ; on a ainsi observé une similitude très élevée. Bien que le nombre moyen des espèces par piège soit plus grand dans les prairies, la diversité est très semblable entre les biotopes. La distribution des espèces les plus abondantes est analysée à deux niveaux : entre pièges (niveau comportemental) et entre biotopes (niveau écologique). Les espèces se distribuaient au hasard pendant une grande partie de l'année, et quand il y a eu agrégation, celle ci fut faible. Au niveau écologique, seul Sphaeridium scarabaeoides a montré une préférence significative pour les prairies, alors que le reste des espèces se distribuait également dans les deux biotopes. On propose que de tels modèles de distribution traduisent le caractère généraliste des Sphaeridiinae autant à petite qu'à grande échelle.

SUMMARY

Pitfall traps baited with cattle dung were used during a year-cycle to study the spatial distribution of severa! species of Sphaeridiinae (Col. Hydrophilidae) in two biotopes (grassland and savanna), from a cattle farm in Chiclana de la Frontera (Cadiz, Spain). Fourteen species were collected, ali of them inhabiting both grassland and savanna, thus, similarity was high between biotopes. The mean number of species per trap was higher in grassland, nevertheless diversity was very similar in the two biotopes. The spatial distribution of the most abundant species was analysed at two different scales: among close traps (distribution at behavioural scale), and habitat selection between grassland and savanna biotopes (distribution at ecological scale). The species were randomly distributed at small spatial scale during most part of the year, aggregation being weak when it occurred. At ecological scale only Sphaeridium scarabaeoides showed a significant selection for grass land, whereas the other species were equally distributed in both biotopes. We propose that such distribution patterns reflect the ecological generalism of Sphaeridiinae, acting from narrow to wide (geographical) scales.

* Departamento de Biologfa Animal y Ecologia. Universidad de Granada. E-18071, Granada, Spain. E-mail: [email protected] ** Dept. Environmental Science & Policy. University of California, Davis. Davis CA, 95616, USA.

Rev. Écol. (Terre Vie), vol. 56, 2001.

37 INTRODUCTION One of the most striking facts concerning coprophilous insects communities is their buge diversity and the high abundance of sorne taxa: according to Hanski & Koskela (1979) more than 50 species and 1 000 individuals may coexist in one individual dung patch. This fact is related to the complex nature of the resource "dung" due mainly to two circumstances: its patchy distribution within the habitats, and the differences (chemical composition, temperature, size ...) among individual patches. Although sorne factors, different from those of ecological, geographical, historical or phylogenetical nature, may influence local diversity of coprophagous beetles (Lobo, 1997), it appears clear that segregation due to interspecific competition is relevant in structuring and diversifying dung beetle communities, although it has been poorly experimentally studied (Hanski, 1991). Species usually segregate using "temporal and spatial refuges" (Giller & Doube, 1994 ), along the time axis (different moments of occurrence) (Finné & Desiére, 1971; Hansk:i & Koskela, 1979; Estrada et al. , 1993), along the spatial axis (inhabiting different places or habitats) (Hanski & Koskela, 1979; Lumaret, 1983), or along the fe eding axis (feeding on severa} types or on different states of degradation of resources) (Landin, 1967; Finné & Desiére, 1971; Koskela, 1972; Sânchez-Pifiero & Avila, 1991; Estrada et al. , 1993; Sowig & Wassmer, 1994). Specialization is, consequently, a valuable way to use such a variable resource. Many other factors may be infiuential in the separation of the species, but the spatio-temporal variation in the occurrence of the species may explain up to 72 % of the differences among dung beetle assemblages (Stevenson, 1982). Thereby, diminishing interspecific competition by means of the allotment of resources among the species, allows the coexistence of species, and therefore a high diversity is favoured. As a consequence of segregation, different patterns of spatial distribution can be found among dung beetles, aggregation dynamics being usual for those more specialized species (Hirschberger, 1998; Palestrini et al. , 1998). Two main scales can be defined to understand spatial distribution of dung beetles. The first of them was called behavioural scale by Hanski (1980b), which involves short-distance movements between patches (i.e. different dung pats) within the same habitat. The second is the scale called ecological (Hansk:i, 1980b), that is, involving movements between patches (i.e. differentbiot opes) far away one from each other. Although these two scales are useful from a practical point of view, we cannot assure that two types of movements (short distance and long distance) do really occur, but rather it is possible that migration from one habitat to another is nothing but an accumulation of short-distance m.ovements, and that habitat-selection is not a consequence of the conditions of the biotope as a whole, but simply of environmental conditions at the microhabitat scale (Hanski & Koskela, 1979); moreover, such a selection may refiect just severa} feeding specializations that promote the distribution patterns of populations. Nevertheless, sorne authors (Stevenson, 1982; Lumaret, 1983) consider the macrohabitat to be a major factor contributing to separate populations of different dung species, and from this point of view, it would be possible that migrations at ecological scale do really occur. On the other band, the spatial patterns of the species may not be the same for males and for females, due to the probably different requirements of both sexes (locating appropriate sites for nesting and development of the larvae, in the case of females, or mating competition, for males). Most of the studies above dealt with Scarabaeoidea dung beetles. They constitute the majority of taxa and individuals in dung and are usually specialized

- 38 - in the use of severa! types or states of dung. Nevertheless, Sphaeridiinae (Hydrophilidae) are one of the most abundant groups in temperate dung beetle communities (Desiére & Thomé, 1977; Hanski, 1980d; Franch et al. , 1990), adults being coprophagous and larvae predators (Boving & Henriksen, 1938; Mohr, 1943; Sanders & Dobson, 1966; Hansk:i, 1980a, 1980c, 1980d; Sowig et al., 1994). Contrary to Scarabaeoidea, they show a wide trophic generalism (Mohr, 1943; Landin, 1957; Rainio, 1966; Landin, 1967; Sowig & Wassmer, 1994) and wide distribution patterns (Chiesa, 1959; Hansen, 1987, 199 1). However, little is known about the biology and ecology of Sphaeridiinae in Iberian Peninsula (Garcfa Camporro & Arradon, 1984; Franch et al., 1990; Romero-Alcaraz et al. , 1997). Taking this into account, in this paper we study the spatial distribution patterns of a non-specialized guild of coprophagous beetles. We expect them not to follow aggregation dynamics due to their trophic generalism, then acting as a large, weil defined, piece of the dung insect community. Thus, the main goals of this paper are: 1) to describe the distribution pattern at small (behavioural) scale of the species of Sphaeridiinae in a location in southern Iberian Peninsula; 2) to test the existence of habitat selection (distribution at ecological scale) by the species of Sphaeridiinae and 3) to explain such distribution patterns according to different ecological fe atures in the study area.

STUDY AREA

The study area is located in south-western Iberian Peninsula, in a coastal location of Cadiz province. The field work was undertaken at a cattle farm in the town of Chi cl ana de la Frontera. Cattle rnoves free during the day ali over the farm, and therefore the cattle pressure and the density of dung is rather homogeneous ali around the area. Samples were taken from two different biotopes: grassland and sa vanna. The main differences between both biotopes are the nature of the soil and vegetation. In the grassland, soils are mainly clayey (clay constituting more than 35 % ), stones being absent, although calcareous nodes are rather common. The soil is very plastic when wet, but becomes rather hard when dry. This type of soil shows a very poor drainage, so areas in which it occurs are usually floodedduring rainy periods. In this biotope, herbaceous and nitrophilous pastures are widely dominant. On the other band, soil from savanna is not weil developed and, which is more relevant, it is covered with a thick sandy stratum, 1-1.5 meters deep. As in the case of grassland, no stone can be found in this biotope. Due to its sandy nature, soil from savanna bas a very high drainage, and is subjected to quick changes of temperature. With regards to vegetation, savanna is a "dehesa" biotope, where pastures are dominant, although shrubs of Pistacia lentiscus L., Calicotome villosa (Poiret) Link, Chamaerops humilis L. and Quercus coccifera L. are also weil developed; sorne oaks (Quercus suber L.) form a very sparse arboreal substratum in this biotope. Temperatures on each sampling date (see below) did not differ between biotopes during the study (air temperature: grassland =

19.06±6.80 °C, S.D.; savanna = 20.05±7.17 oc; F = 1.22; p = 0.27; d.f. = 1, 195; soil temperature: grassland = 20.1 7±8.47 oc; savanna = 21.26±10.15 oc; F = 0.42; p = 0.52; d.f. = 1, 195; one-way ANOVA, data log-transformed). It is remarkable that the whole study area constitutes a habitat mosaic in which grassland and savanna patches are sometimes very close, about 150 meters as a minimum.

- 39 - METHODS

Dung-baited pitfall traps (Lobo et al., 1988; Veiga et al., 1989), were used in both biotopes to collect dung beet1es from February 1987 to January 1988. Every month and at the same date, one set of ten traps was placed at each biotope. Traps were placed on the ground along three parallel rows of 3, 4 and 3 traps respectively, traps being 4 meters away from each other (Fig. 1). Each trap consisted in a cylindrical pot (180 mm diameter, 200 mm high) buried in the ground, containing a plastic bag which allowed a quick and clean collection of the content. The bag contained 400 cm3 of a preservation solution (chloral hydrate 10 g/1.).A grid of 25 x 25 mm mesh was placed at the top of each trap, acting as a support for the bait. This was 1 1 of fresh cow dung, previously examined to avoid the presence of any insect before it was placed on the grid. In the analysis we considered each individual trap (also called single patch in the text) to be a sample.

4�4m (j)/ 0 �0 0 0 0 0 ® Figure 1. - The ten traps in a set. lndividual traps were 4 rn apart from each of their inmediate neighbours.(j)

Diversity of Sphaeridiinae in each biotope was measured by means of the a index of logarithmic series (Magurran, 1988). The quantitative Morisita-Hom index (Magurran, 1988) was utilized to calculate similarity between grassland and savanna according to their faunistic composition. Spatial distribution of the most abundant species was studied at two different scales, distribution between the two biotopes (grassland and savanna), which enables to know whether there is any kind of habitat selection, and distribution among dung patches within the same set of traps. In the first case, the existence of possible differences in the mean number of individuals per trap between biotopes was analysed for each species, using the Mann-Whitney non parametric test.

- 40 - Distribution patterns among close patches was determined at each habitat and sampling date using the index of Green (IG) (Ludwig & Reynolds, 1988). The index was calculated from the expression IG =(ID - 1) 1 (n - 1), where ID is the relative variance (variance/mean abundance per patch), and n is the total abundance in the set of traps. lt is accepted that one distribution is lightly aggregate for values of IG close to 1, while if IG is near 0 then the distribution is accepted to be random. In order to separate both tendencies (towards random and aggregate distributions) the value of iG = 0.17 was assumed to be critical (Ludwig & Reynolds, 1988). Differences in the mean number of species per trap between both biotopes were also measured using the Mann-Whitney U test, so aggregation of species among single patches in the same biotope was quantified the same way used for individuals of one single species. In all cases at this short scale (distribution of species and distribution of individuals of each species) only cases in which sample size was 10 or more were considered. We assumed that IG is equal to zero (i.e. random distribution) when sample size was less than 10. We have followed the taxonomie criteria of Chiesa (1959), Hansen (1987, 1991) and Berge Henegouwen (1989).

RESULTS

NUMBER OF SPECIES AND DIVERSITY

A total number of 2 302 specimens of 14 species of Sphaeridiinae were collected, belonging to the genera Cercyon Leach (9 species), Sp haeridium F.

TABLE I

List of sp ecies collected during the study with abundance (AB.) and percentage (%) of each sp ecies in each biotope and in total.

Species Grass land Savanna Total

AB. % AB . % AB . % Sp haeridium bipustulatum F., 1775 640 57.19 895 75.66 1 535 66.68 S. marginatum F., 1787 71 6.34 56 4.73 127 5.52 S. scarabaeoides L., 1758 44 3.93 2 0.17 46 2.00 S. lunatum F. , 1792 2 0.18 1 0.08 3 0. 13 Cercyon haemorrhoidalis F., 1775 161 14.39 103 8.71 264 11.47 C. quisquilius L., 1761 143 12.78 99 8.37 242 10.51 C. unipunctatus L., 1761 23 2.06 6 0.51 29 1.27 C. melanocephalus L., 1758 11 0.98 4 0.35 15 0.66 C. atricapillus Marsham, 1802 2 0.18 7 0.59 9 0.39 C. arenarius Rey, 1885 4 0.36 3 0.25 7 0.30 C. lugubris Olivier, 1790 3 0.27 3 0.25 6 0.26 C. nigriceps Mulsant, 1802 2 0.18 1 0.08 3 0.13 C. lateralis Marsham, 1802 1 0.09 2 0.17 3 0.13 Cryptopleurum minutum Mulsant, 1844 12 1.07 1 0.08 13 0.55 Total 1 119 100 1 183 100 2 302 100

- 41 (4 species) and Cryptopleurum Mulsant (1 species). Inventories of species were the sarne at both biotopes, and also abundances were similar, as it is shown in table 1. This fact showed a very high faunistic similarity between grassland and savanna (Morisita-Hom index = 0.96). Diversity was also very similar in both biotopes (a grassland = 2.25; a savanna = 2.23; a total = 1.98).

SMALL- SCALE DISTRIBUTION

Six species were abundant enough to enable the study of their spatial distribution among traps: Sphaeridium bipustulatum F., S. marginatum F., S. s carabaeoides L., Cercyon haemorrhoidalis F., C. quisquilius L., and C. unipunc tatus L. Distribution among close dung patches differed at different months of the year, moments in which aggregation occurred being different for each species. For ail the collected fourteen species considered either together or separately, results showed that in all cases but two (January in grassland: IG = 0.381, and June in savanna: IG = 0.230) species were randomly distributed among the pats in a single set of traps (IG < 0. 17) (Fig. 2). Figs. 3, 4, 5, 6, 7 and 8 represent the values of IG obtained for the most abundant species, in the months when the number of specimens was high enough to make the analysis possible, together with their respective abundances in different months. Mainly random distributions can be surmised for the species of Sphaeridiinae among closely located pats during the major part of their period of occurrence (I.G. < 0. 17, when it was possible to calculate it). Only in the species Cercyon haemorrhoidalis (Fig. 6) and C. quis quilius (Fig. 7) moments in which distribution was different from random were found. In C. haemorrhoidalis, aggregate distribution was found to occur in

3.5 0.40 � N° species

3.0 -<>- Index of Green 0.35

0.30 2.5 Cl) w 0.25 z ü w � 2.0 w Cl) 0.20 � u. 0 1.5 u. 0::: 0.15 w � co 1.0 0 :::!!: 0.10 ::> � z 0.5 0.05

0.00 0.0 Grassland Savanna JFMAMJ J ASOND J FMAMJJASOND

Figure 2. - Mean number of species per pat and aggregation of species (index of Green) in both grassland and savanna during the study period. Critical value of IG (0. 17) is represented by the horizontal line.

- 42 - 35 0.20 Sphaeridium bipustulatum 0.18 30 0.16 ...�z .. Abundance 25 -o- Index of Green 0.14 z 20 0.12 w w w 0 a: z 0.10 Cl <( 0 15 u. z 0.08 0 :::> al <( 10 0.06 �0 � 0.04 5 0.02 0 0.00

JFMAMJ JASOND JFMAMJ JASOND

Figure 3. - Aggregation in Sphaeridium bipustulatum. Abundance (mean number of individuals per trap) and aggregation (index of Green) in both grassland and savanna during the study period are shown. Critical value of IG (0.17) is represented by the horizontal line.

3.0 0.20 Sphaeridium marginatum 0.18 2.5 0.16 -ir- Abundance Index Green 2.0 -o- of 0.14 z 0.12 w w w 0 1.5 a: z 0.10 Cl <( 0 u. z 0.08 0 :::> 1.0 >< al w <( 0.06 0 � 0.5 0.04

0.02 0.0 000000000000 0.00 Savanna JFMAMJ JASOND

Figure 4. - Aggregation in Sp haeridium marginatum. Legend as in Fig. 3.

43 2.5 0.20 Sphaeridium scarabaeoides 0.18

------···-----Ï------·------·-·------·--··-·--·--·-----··- 2.0 0.16 fl ··-A··· Abundance ii 0.14 Index Green : i of 1.5 z � � 0.12 w w w ü l i 0:: z i i 0.10 C) <( : : 0 1.0 i i u. z : i: 0.08 0 ::::> ID <( 0.06 0� 0.5 1 \: � A : 0.04

0.02 li /�l-� .b··A 0.0 Jl'' bn/z••/:.••/t' � 0.00

JFMAMJ J ASOND JFM AMJ JASOND

Figure 5. - Aggregation in Sp haeridium scarabaeoides. Legend as in Fig. 3.

10 Cercyon haemorrhoidalis 0.9

0.8 ...�z ... Abundance 8 0.7 - x ID 0.3 w <( 0 � 2 0.2

0.1

0 0.0 Grassland Savanna

JFMAMJ J ASOND JFMSMJ JASOND

Figure 6. - Aggregation in Cercyon haemorrhoidalis. Legend as in Fig. 3.

- 44 - 3.5 Cercyon quisquilius � ••êoo• Abundance 0.5 3. 0 � � lnd.Green n . . t .�=··i 2.5 �\ 0.4 ! i ! \ i z 2.0 1 w w : : ,i 0.3 w () i i tt: z C) 1.5 u. (§ i \ 0 z � _,-,1 0.2 ::> 1 i ro �------� <( 1.0 } � + \ : 0 � 0.1 0.5 0.0 ~ 0.0 Grassland Savanna

JFMAMJ J ASOND JFMAMJ JASOND

Figure 7. - Aggregation in C. quisquilius. Legend as in Fig. 3.

3.0 0.20 Cercyon unipunctatus 0.18 2.5 0.16 .. ë... Abundance Index Green 0.14 2.0 1 -o- of z 0.12 w w w () 1.5 0.10 tt: z 1 C) <( u. 0 0.08 0 z ::> 1.0 x ro 0.06 w <( 0 � 0.04 0.5 l 0.02 0.0 � � 0.00 Grassland \ Savanna JFMAMJ JASOND JFMSMJJ ASOND

Figure 8. - Aggregation in Cercyon unipunctatus. Legend as in Fig. 3.

- 45 - December both in grassland (IG = 0.820) and in savanna (IG = 0.232). C. quis quilius exhibited aggregate distribution in June, August and December, always in grassland (IG June = 0.507; IG August = 0.173; IG December = 0.304). In general, moments with significant aggregation coincided with those when populational maxima were reached: when it was possible to make correlations (Spearrnan non parametric correlation) between population (mean abundance per trap) and aggregation (IG) through the year (at least in one month IG > 0), significant correlations between both variables were obtained in the cases of S. bipustulatum in both grassland and savanna (R = 0.69; p < 0.01 and R = 0.83; p < 0.001, respectively), Cercyon haemorrhoidalis in both grassland and savanna (R = 0.65 ; p < 0.05 and R = 0.65; p < 0.05, respectively) and C. quisquilius in both grassland (R = 0.82; p < 0.001) and savanna (R = 0.65 ; p < 0.05).

HABITAT SELECTION

The mean number of species per patch was rather low in both biotopes (grassland: 1.79 ± 1.33; savanna: 1.32 ± 1.05), but it was significantly higher in grassland (p = 0.012, Mann-Whitney U test). The maximum number of species in a single patch was 5 in grassland and 4 in savanna. Besides the six abundant species mentioned above, another two species, C. melanocephalus L. and Crytopleurum minutum Mulsant, were abundant enough throughout the whole year to quantify their distribution between biotopes. For these species data from captures in both biotopes were submitted to the Mann-Whitney U test, which results are shown in Fig. 9. No significant preference for any of the two habitats can be inferred from the results in any of the eight species of the study area, except for Sp haeridium scarabaeoides, that showed a significant selection for the grassland biotope (mean number of individuals per trap: grassland: 0.29 ± 0.85; savanna: 0.01 ± 0.09; p < 0.001). The other seven species did not show significant differences of mean abundance between biotopes, although Cercyon haemorrhoidalis, C. unipunctatus and Cryptopleurum minutum were close to statistical significance (p = 0.09).

DISCUSSION

DISTRIBUTION AMONG CLOSE PATCHES

Mainly random distribution of the species and populations of Sphaeridiinae among close dung patches can be inferred from our results during the greater part of their period of occurrence. Distribution at a short spatial scale of species of the genus Sp haeridium has been previously studied (Otronen & Hanski, 1983), and it has been found that populations reach the free-ideal distribution and that the distributions of species usually overlap, just because individuals occupy all those dung patches appearing to be more adequate in order to be colonized. Giller & Doube (1994) described a similar distribution for sorne Scarabaeidae beetles from South Africa. Moreover, this model of distribution was a foregone result due to the fact that coprophilous hydrophilid beetles are known to be microhabitat generalists (Hanski, 1980b), not only in the sense of feeding on different kinds of dung (Landin, 1957; Rainio, 1966), but also inhabiting many other kinds of decaying organic matter (Hansen, 1987; 1991).

- 46 - 20 Q. � 18 ::C: St Dev. 1- Grassland a:: 16 D w - Savanna Q. en 14 ...J <( :::1 12 0 5 10 i5 � 8 u.. 0 a:: 6 w Ill ::::!ë 4 :::1 z z 2 � :::E 0 S.bip S.mar S.sca C.hae C.qui C.uni C.mel C.min

Figure 9. - Mean number of individuals per trap in each biotope of the eight most abundant species and values of the Mann-Whitney U test; *: p < 0.001; ns: non significant. Abbreviations: S. bip: Sphaeridium bipustulatum; S. mar: S. marginatum; S. sca: S. scarabaeoides; C. hae: Cercyon haemorrhoidalis; C. qui: C. quisquilius; C. uni: C. unipunctatus; C. mel: C. melanocephalus; C. min: Cryptopleurum minutum.

In general in this study, significant aggregation coïncides with populational maxima. This may have a double explanation: on one band, when populations reach a high number of individuals, mating between males and females may occur only on the most adequate pats in order to allow properly both nesting and development of larvae. On the other band, but closely related to previous aggregation for mating and oviposition, as a consequence of the development of larvae on sorne particular dung pats but not on others, aggregation may be due to congregation of new emerging adults on those patches. Therefore, until the moment of dispersal of tho se new adults, high aggregation indices may occur. Data about distribution of eggs and larvae among close dung pats, probably affected by competition or predation (Hanski, 1987), are required to understand the aggrega tion dynamics found in this study. But these reproduction-related events affecting aggregation processes through differentmoments of the year are expected to occur in Sphaeridiinae, due to the fact that, contrary to most Hydrophilidae, they usually have more than one generation per year, often three or more (Hansen, 1987).

HABITAT SELECTION

Mean number of species per patch was higher in grassland than in savanna, this was probably due to the greater abundance (but not significantly greater) of sorne species of Sphaeridiinae in grassland, such as Cercyon haemorrhoidalis, C. unipunctatus and Cryptopleurum minutum. The low abundance of the two latter species mak:es difficult to correctly explain their real trend in regard to habitat

- 47 - selection, but we cao assure that, in general, no marked preference for any biotope is shown by the Sphaeridiinae of Chiclana (Fig. 2), except by Sphaeridium scarabaeoides (Fig. 5). This result contrasts with those of other studies, in which species have been observed to associate with open habitats, their populations dirninishing to large extent in shrubby or forest areas (Rainio, 1966; Hanski, 1980a). Furthennore, in general no tendency to modify such distribution along the temporal axis was found (Hanski, 1980b). This absence of preference in the Sphaeridiinae we studied could be explained by two different hypotheses: 1) differences between both biotopes are not marked enough to displace the preferences of the species towards one or the other biotope, and 2) although these differences do exist, the species cao easily move from one biotope to the other, so that the structure of their populations does not vary at that spatial scale. With regards to the first hypothesis, three features of the biotope may influencethe community and the distribution of the species of coprophilous beetles (Koskela & Hanski, 1977). The first one is the rnicrohabitat density within the biotope (the number of adequate patches for colonization within a rather homogeneous biotope). In our study both biotopes support sirnilar cattle pressure, and therefore density of cattle dung pats is sirnilar in both. This factor, theo, is not expected to determine any significant differences in the faunistic composition of the two habitats. The second feature is the rnicroclimate of macrohabitat. This is mainly deterrnined by temperature: in general, high temperature will result in an increase of abundances and diversity. But there were no difference between temperature in both biotopes, so a lack of difference between grassland and savanna's communities of Sphaeridiinae cao be expected. The last feature is the macrohabitat structure: differences in the degree of exposition to sunlight and the nature of the soil, which is important in deterrnining the conditions of the dung patch, are the two main characteristics of biotopes that we must discuss here. Different expositions to sunlight may cause changes in the physical evolution of the dung through time, which may determine the existence of different entomo logical communities between very exposed and covered sites. At the same time, and given that localisation and orientation towards the dung by coprophagous beetles is basically olfactory, plant cover may interfere, acting as a barrier against scent spreading. Therefore, a more or less open habitat is supposed to be better than a more closed one for coprophilous species (see Lumaret, 1983). Certainly, vegetation of grassland and savanna are quite different, but both biotopes cao be easily rated as open habitats, so macrohabitat structure would no be expected to induce any difference between grassland and savanna's communities of Sphaeri diinae. Therefore, the nature of the soil is the only factor that may influence the movements of Sphaeridiinae between habitats, just because grassland is expected to be more adequate for coprophilous fauna. Hurnidity loss is lower in those pats in the grassland, due to a soil fundamentally constituted of clay. Therefore, those pats cao be utilised for a longer period of time than in sa vanna, which get dry more quickly. In fact, sorne Scarabaeidae and Aphodiidae species have been found to show a marked tendency towards either grassland or savanna in our study area (Âvila et al., 1989; Avila & Sânchez-Pifiero, 1990), as a consequence of soil nature. Nevertheless, the observed fact is that, in general, the species we are dealing with do not select any biotope, so the second hypothesis mentioned above appears to be the most valid, i.e. the ability of species to migrate may determine whether they cao or not equally use the different biotopes. The fact that Sp haeridium scarabaeoides showed a significant preference for grassland, may be

- 48 due to this species having a worse dispersal capability, which has been already described (Otronen & Hanski, 1983), at least in a context in which competition probably involves an important limitation. In addition, Sp haeridium scarabaeoides appears to be very sensitive to the competition with other Sp haeridium species, which restricts its phenology to a short period, different from that in other neighbour regions (Romero-Alcaraz et al. , 1997). Probably such limitations lead S. scarabaeoides to preferentially inhabit grasslands, thereby getting the advan tages cornmented above, but it cannot develop on a less adequate biotope, as sava nna. Lastly, something must be said about the widest scale of spatial distribution that can be studied in any organism, that is its geographical distribution. Ali the species collected during our study are widely distributed (Chiesa, 1959; Hansen, 1987, 1991), most of them over the whole Palearctic region and successfully introduced in the Neacrtic region (Sphaeridium bipustulatum, S. marginatum, S. scarabaeoides, S. lunatum, Cercyon haemorrhoidalis, C. quisquilius, C. uni punctatus and Cryptopleurum minutum). Cercyon arenarius exhibits the narrowest distribution area, but even this species is well-distributed throughout the Mediter ranean area. This fact is something usual among Sphaeridiinae not only in temperate regions, but also in tropical areas (Berge Henegouwen, 1992). Accord ing to Lobo (1993), when considering data from annual sampling, temperate species with greatest frequencies in dung pats are those with wider ecological capability, but not greatest abundances. This is due to the fact that in temperate regions seasonality is usually a major factor for dung beetles (Hanski & Koskela, 1977; 1979 Hanski, 1980a). Because many geographically restricted species occur during a brief period of time showing high abundances, there is not a necessary relationship between abundance and wide distribution. Moreover, many species may have very low local abundance but a wide distribution. This is the case of Sphaeridiinae from our site, where most of the species are scarce, but widely distributed. Afterhaving studied the spatial distribution of Sphaeridiinae at smaller scales, it is possible to think that the wide geographical distribution of these species just refiects their weil developed capability of dispersal and their high trophic generalism (Mohr, 1943; Landin, 1957; Rainio, 1966; Landin, 1967; Sowig & Wassmer, 1994), which probably favours the spreading of the species at a local or regional scale (Lobo, 1993) as they can easily move among different dung patches (sometimes of different nature) and among different habitats.

CONCLUDING REMARKS

Sphaeridiinae from our study area did not show, in general, any preference for grassland or savanna, although the nature of the soil, which may influence the quality of the dung, is clearly different between both biotopes. Species were randornly distributed among pats at each biotope, and aggregation, when occur ring, being slight, and probably related to reproductive events. These facts are probably related with the feeding generalism of the species, which, contrary to many other coprophilous species, can easily inhabit different dung habitats and for which the quality of the dung is not a major factor for feeding and developing. The lack of dung selection by these species may be in the base of the similarity of cornmunities in both biotopes, and also is probably related with the wide distribution area (at geographical scale) of the species in the area.

- 49 - ACKNOWLEDGEMENTS

We thank Dr. Abdelmounim Badih (University of Granada) for his advice in French. Two anonymous referees contributed to improve an earlier version of the manuscript.

REFERENCES

A viLA, J.M. & SANCHEZ-PiNERO, F. (1990). - Contribuci6n al conocirniento de las comunidades de escarabeidos copr6fagos de Chiclana de la Frontera (Cadiz, Espaiia). Farnilia Aphodiidae. (Coleoptera, Scarabaeoidea). Zoologica baetica, 1: 147-164. ÂVILA, J.M., SANCHEZ-PINERO F., & PASCUAL, F. (1989). - Sobre los Scarabaeoidea (Col.) copr6fagos de Chiclana de la Frontera (Cadiz, Espaiïa). Farnilia Scarabaeidae. Anales de Biologfa, 15 (Biologfa Animal, 4), (1988) 1989: 59-71. BERGE HENEGOUWEN, A.L. VAN (1989). - Sp haeridium marginatum reinstated as a species distinct from S. bipustulatum (Coleoptera: Hydrophilidae). Ent. Ber. Amst. , 49 (Il): 168-170. BERGE HENEGOUWEN, A.L. VAN (1992). - Notes on the genus Sp haeridium Fabricius in tropical Africa with descriptions of three new species. (Coleoptera: Hydrophilidae, Sphaeridiinae). Storkia, 1: 14-24. BbviNG, A.G. & HENRIKSEN, K.L. (1938). - The development stages of Danish Hydrophilidae (lns. Coleoptera). Vidensk Meddl Dansk Naturhistori Forening, 102: 27-162. CHIESA, A. (1959). - Hydrophilidae europae. Coleoptera palpicornia. Ta belle di determinazione. Arnaldo Forni Ed., Bologna. DESIÉRE, M. & THOMÉ J.P. (1977). - Variations qualitatives et quantitatives de quelques populations de coléoptères coprophiles associées aux excréments de trois types d'herbivores. Revue Écologie Biologie Sol, 14: 583-591. ESTRADA, A., HALFFIER, G., COATES-ESTRADA, R. & MERITT, D.A. (1993). - Dung beetles attracted to marnmalian herbivore (Alouatta palliata) and omnivore (Nasua narica) dung in the tropical rain forest of Los Tuxtlas, Mexico. Journal of Trop ical Ecolo gy, 9: 45-54. F'INNÉ, D. & DESIÉRE, M. (1971). - Étude synécologique des bouses de Bovidés. I. - Évolution estivale de la biomasse des Coléoptères en fonction du vieillissement des bouses. Revue Écologie Biologie Sol, 8: 409-417. FRANCH, J., DOMÉNECH, J. & SANCHEZ-CABRERO, C. (1990). - La succesi6 d'invertebrats en las buines de vaquf a la vall d' Aisa (Pirineu aragonés). Orsis, 5: 113-134. GARCÏA-CAMPORRO, C. & ANADON, R. (1984). - Variaci6n de la comunidad de cole6pteros copr6fagos (Hydrophilidae y Scarabaeidae) a Jo largo del proceso de descomposici6n de la boiiiga. Revista Biolog{a Universidad Oviedo, 2: 143-153. GILLER, P.S. & DoUBE, B.M. (1994). - Spatial and temporal co-occurrence of competitors in Southern African dung beetle comrnunities. Journal of Animal Ecology, 63: 629- 643. HANSEN, M. (1987). - The Hydrophilidae (Coleoptera) of Fennoscandia and Denmark. Fauna Entomologica Scandinavica, 18: 124-165. HANSEN, M. (1991). - The Hydrophiloid beetles, Phylogeny, Classification and a Revision of the Genera (Coleoptera, Hydrophiloidea). Biologiske Skrifter 40, Copenhagen. HANSKI, 1. (l980a). - The comrnunity of coprophagous beetles (Coleoptera, Scarabaeidae and Hydrophilidae) in northern Europe. Annales Entomologica Fennica, 46: 57-73. HANSKI, 1. (l980b). - Spatial patterns and movements in coprophagous beetles. Oikos, 34: 293-310. HANSKI, 1. (1980c). - Migration to and from cow droppings by coprophagous beetles. Annales Zoologici Fennici, 14: 204-223. HANSKI, I. (1980d). - Patterns of beetle successions in droppings. Annales Zoologici Fennici, 17:17-25. HANSKI, I. (1987). - Colonization of ephemeral habitats. Symposium of the British Ecological Society, 26: 155-185. HANSKI, 1. (1991). - The dung insect community. Pp.5- 21, in: 1. Hansk:i & Y. Cambefort (eds). Dung Beetle Ecology. Princeton University Press, Princeton. HANSKI, I. & KOSKELA, H. (1977). - Niche relations among dung-inhabiting beetles. Oecologia, 28: 203-23 1. HANSKI, 1. & KosKELA, H. (1979). - Resource partitioning in six guilds of dung-inhabiting beetles (Coleoptera). Annales Entomologica Fennica, 45: 1-12. HIRSCHBERGER, P. (1998). - Spatial distribution, resource utilisation and intraspecific competition in the dung beetle Aphodius ater. Oecologia, 116: 136-142.

50 KOSKELA, H. (1972). - Habitat selection of dung-inhabiting Staphylinids (Coleoptera) in relation to age of the dung. Annales Zoologici Fennici, 9: 156-171. KoSKELA, H. & HANSKI, 1. (1977). - Structure and succession in a beetle community inhabiting cow dung. Annales Zoologici Fennici, 14: 204-223. LANDIN, B.A. (1957). - Lamellicornia. Svensk Insecktfauna 46. Uppsala. LANDIN, J. (1967). - On the relationship between the microclimate in cow droppings and sorne species of Sp haeridium (Col. Hydrophilidae). Op uscula Entomologica, 33: 207-212. LOBO, J.M. (1993). - The relationship between distribution and abundance in a dung-beetle comrnunity (Col., Scarabaeoidea). Acta Oecologica, 14: 43-55. LOBO, J.M. (1997). - Influencias geogrâficas, hist6ricas y filogenéticas sobre la diversidad de las comunidades locales: una révision y algunos ej emplos utilizando Scarabaeoidea copr6fagos (Coleoptera, Laparosticti). Bolet(n Asociaci6n espanola Entomologfa, 21: 15-31. LOBO, J.M., MARTIN-PIERA, F. & VEIGA, C.M. (1988). - Las trampas pitfall con cebo, sus posibilidades en el estudio de las comunidades de Scarabaeoidea (Col.). 1. Caracterfsticas determinantes de su capacidad de captura. Revue Écologie Biologie Sol, 25: 77- 100. LUDWIG, J.A. & REYNOLDS, J.F. (1988). - Statistical Ecology. Wiley Interscience, New York. LUMARET, J.P. (1983). - Structure des peuplements de Coprophages Scarabaeidae en région méditerranéenne française: relation entre les conditions écologiques et quelques paramètres biologiques des espèces. Bulletin de la Societé entomologique de France, 88: 481 -495. MAGURRAN, A.E. (1988). - Ecological diversity and its measurement. Princeton University Press, Princeton. MOHR, C.O. (1943). - Cattle droppings as ecological units. Ecological Monographs, 13: 275-309. ÜTRONEN, M. & HANSKI, 1. (1983). - Movements patterns in Sp haeridium: differences between species, sexes, and feeding and breeding individuals. Journal of Animal Ecology, 52: 663-680. PALESTRINI, C., 8ARBERO, E. & ROLANDO, A. (1998). - lntra- and interspecific aggregation among dung beetles (Coleoptera: Scarabaeoidea) in an Alpine pasture. Journal of Zoology, 245: 101-109. RAINIO, M. (1966). - Abundance and phenology of sorne coprophagous beetles in different kinds of dung. Annales Zoologici Fennici, 3: 88-98. ROMERO-ALCARAZ, E., SANCHEZ-Pil'mRO, F. & ÂVILA J.M. (1997). - Los Sphaeridiinae (Coleoptera, Hydrophilidae) en una zona del suroeste ibérico. 1: Composici6n faunfstica y fenologfa. Boletfn Asociaci6n espanola Entomologfa, 21: 22 1 -235. SANCHEZ-PINERO, F. & ÂVILA, J.M. (1991). - Analisis comparativo de los Scarabaeoidea (Coleoptera) copr6fagos de las deyecciones de conejo [Oryctolagus cuniculus (L.)] y de otros mamfferos. Estudio preliminar. Eos, 67: 23-34. SANDERS, D.P. & DOBSON, R.C. (1966). - The insect complex associated with bovine manure in Indiana. Annals of the Entomological Society of America, 59: 955-959. SOWJG, P. & W ASSMER, T. ( 1994). - Resource partitioning in coprophagous beetles from sheep dung: Phenology and microhabitat preferences. Zoologische Jahrbücher, Abteilung Systematik, 121: 171-192. SOWIG, P., HIMMELBACH, W. & HIMMELSBACH, R. (1994). - Sp haeridium-Larven (Coleoptera, Hydrophilidae) ais Priidatoren der Maden von Musca autumnalis. Der Einflub der Witterung auf ein temporares Riiuber-Beute-System. Ve rhandlungen der Deutschen Zoologischen Gesellschaft, 87: 315. STEVENSON, B.G. (1982). - The hutchinsonian niche: Multivariate statistica1 analysis of dung beetle niches. The Coleopterists Bulletin, 36: 246-249. VEIGA, C.M., LOBO, J.M. & MARTÏN-PIERA, F. (1989). - Las trampas pitfall con cebo, sus posibilidades en el estudio de las comunidades copr6fagas de Scarabaeoidea (Col.). II: Anâlisis de efectividad. Revue Écologie Biologie Sol, 26: 91-109.